Showing papers in "Surface & Coatings Technology in 1999"

Plasma electrolysis for surface engineering

Abstract: This paper overviews the relatively new surface engineering discipline of plasma electrolysis, the main derivative of this being plasma electrolytic deposition (PED), which includes techniques such as plasma electrolytic oxidation (PEO) and plasma electrolytic saturation (PES) processes such as plasma electrolytic nitriding/carburizing (PEN/PEC). In PED technology, spark or arc plasma micro-discharges in an aqueous solution are utilised to ionise gaseous media from the solution such that complex compounds are synthesised on the metal surface through the plasma chemical interactions. The physical and chemical fundamentals of plasma electrolysis are discussed here. The equipment and deposition procedures for coating production are described, and the effects of electrolyte composition and temperature on ignition voltage, discharge intensity and deposited layer thickness and composition are outlined. AC-pulse PEO treatment of aluminium in a suitable passivating electrolyte allows the formation of relatively thick (up to 500 μm) and hard (up to 23 GPa) surface layers with excellent adhesion to the substrate. A 10–20 μm thick surface compound layer (1200HV) and 200–300 μm inner diffusion layer with very good mechanical and corrosion-resistant properties can also be formed on steel substrates in only 3–5 min by use of the PEN/PEC saturation techniques. Details are given of the basic operational characteristics of the various techniques, and the physical, mechanical and tribological characteristics of coatings produced by plasma electrolytic treatments are presented.

A novel pulsed magnetron sputter technique utilizing very high target power densities

Abstract: Using a novel pulsed power supply in combination with a standard circular flat magnetron source, operated with a Cu target, a peak power density of 2800 W cm -2 was achieved. This results in a very intense plasma with peak ion current densities of up to 3.4 A cm −2 at the substrate situated 10 cm from the target. The ionized fraction of the deposited Cu flux was estimated to be approximately 70% from deposition rate measurements. The potential for high-aspect-ratio trench filling applications by high power pulsed magnetron sputtering is demonstrated by deposition in via-structures. The high power pulsed technique also results in a higher degree of target utilization and an improved thickness uniformity of the deposited films compared with conventional d.c. magnetron sputtering.

Kinetic spray coatings

Abstract: Coatings have been produced by entraining metal powders in an air flow which is accelerated by a de Laval type of nozzle. The particles are not melted or thermally softened prior to impingement onto the substrate. The coating process depends primarily on the kinetic energy of the incident powders. The coatings have low oxide content and low thermal stress, and can exhibit relatively low porosity and high adhesion. The mechanism by which the coatings are formed is not well understood, and it is the goal of this work to provide some insights into this mechanism. We have produced a new high-velocity spray apparatus which allows the spray parameters to be controlled and monitored for the first time. This, together with our simulations of air and particle velocities and temperatures, has provided new information on the coating process. Al, Cu, and Fe powders were sprayed onto Al, brass, Cu, and steel substrates. A threshold behavior was observed for coating deposition as a function of nozzle inlet air temperature, with a roughly linear behavior above the threshold. Results are obtained as a function of nozzle inlet air pressure and temperature, powder feed rate, and nozzle–substrate stand-off distance. The effect of the choice of substrate metal was relatively weak in our experiments. Results seem consistent with necessary inelastic processes such as plastic deformation and/or partial melting of the powder particles upon collision with the substrate. More research is needed to define the relative importance of these phenomena or of other possible mechanisms.

Nanocomposite tribological coatings for aerospace applications

Abstract: Challenges in aerospace tribology and composite coatings for aerospace applications are briefly reviewed. Attention is given to nanocomposite coatings made of carbide, diamond-like carbon (DLC) and transition-metal dichalcogenide phases. The preparation of such coatings within the W–C–S material system using a hybrid of magnetron sputtering and pulsed laser deposition is described. Coatings consist of 1–2 nm WC and 5–10 nm WS2 grains embedded in an amorphous DLC matrix. These WC/DLC/WS2 nanocomposites demonstrate low friction and wear in tests performed in high vacuum, dry nitrogen and humid air. Coatings are found to adapt to the test conditions, which results in: (1) crystallization and reorientation of initially nanocrystalline and randomly oriented WS2 grains; (2) graphitization of the initially amorphous DLC matrix; (3) reversible regulation of the composition of the transfer film between WS2 and graphite with environmental cycling from dry to humid; and (4) possible DLC/WS2 synergistic effects, providing friction reduction in oxidizing environments. These adaptive mechanisms achieve low friction coefficients of 0.02–0.05 and an endurance above two million cycles in space simulation tests. This also provides stable coating performance and recovery of low friction in tests simulating ambient/space environmental cycling. Correlations among WC/DLC/WS2 chemistry, structure, hardness, friction and wear are discussed. The tremendous potential of such composites for aerospace tribology is demonstrated.

Thickness effects on the mechanical properties of micro-arc discharge oxide coatings on aluminium alloys

Abstract: Weight-saving materials are becoming increasingly important, especially in the automotive and aerospace industries. Design engineers would thus like to make more extensive use of light metals such as aluminium, titanium, magnesium and their alloys; however, these materials tend to have poor wear resistance. Previous treatments and coatings applied to aluminium alloys, for example by traditional processes such as hard anodising and thermal spraying, have suffered from the low load support from the underlying material and/or insufficient adhesion, which reduces their durability. Also, although TiN-, CrN- or DLC-coated aluminium alloys (using various PVD methods) can achieve a high surface hardness, in practice they often exhibit poor performance under mechanical loading, since the coatings are usually too thin to protect the substrate from the contact conditions. In the work reported here, a plasma electrolysis technique known as micro-arc discharge oxidation (MDO) was investigated; thick and hard oxide ceramic layers were fabricated on BS Al-6082 aluminium alloy by this method. The phase composition and microstructure of the MDO coatings were investigated by XRD, SEM and EDX analyses. A number of adhesion and tribological sliding and impact wear tests were also performed. It was found that Al–Si–O coatings with a hardness of up to 2400 HV and with excellent wear resistance and load support could be formed. The thickness of the coatings significantly influenced the mechanical properties. In terms of tribological performance, the thicker coatings performed best in sliding, scratch and impact tests whilst thin coatings were also surprisingly effective in both impact and low-load sliding. Coatings of intermediate thickness provided relatively poor performance in all tribological tests.

The evolution of thermal barrier coatings — status and upcoming solutions for today's key issues

Abstract: Thermal barrier coating applications have been used on thermally loaded combustion process components for decades. In the beginning of turbine technology development, science and industry worked on solutions about how to combine different properties such as those of superalloy metals and ceramic insulators. While partially stabilized zirconia became the standard material very early on, thermal spraying and electron beam physical vapor deposition in the early 1990s were even considered as competing technologies. This paper reviews why EB-PVD is the actual choice for the latest state-of-the-art components. Although EB-PVD coatings have a higher thermal conductivity than plasma-sprayed coatings, especially for parts in the HP stage of the turbine, they have a longer life and are statistically more reliable. The major roadblocks for thermal barrier technology on its way to become a fully prime reliant, designed-in feature are the understanding and modeling of failure mechanisms and consequently to prove the developed lifing-models by testing and ultimately real component performance. Several potential answers for today's technical issues are discussed with respect to their ability to shift TBC applications to the next level of reliability within various engine environments. For example, the inline hardware concept offers a unique combination of conservative, proven process sequence steps with widely improved quality aspects and optimized throughput set-ups.

Plasma nitriding of stainless steels at low temperatures

Abstract: To avoid the drop in corrosion resistance of stainless steels in conventional nitriding (precipitation of CrN), low-temperature techniques like ion implantation, plasma immersion ion implantation (PIII, PI3) and low-temperature plasma nitriding were developed. In this investigation, four stainless-steel grades (ferritic: X6Cr17, austenitic–ferritic: X2CrNiMoN22.5.3, austenitic: X8CrNiTi18.10 and X5CrNi18.10) were plasma-nitrided between 250 and 500°C. Nitrogen-enriched layers with a high nitrogen content were produced, leading to a significant increase in surface hardness. X-ray diffraction indicated that CrN did not precipitate if treatment temperatures did not exceed 400°C. ‘Expanded austenite’ formed in the austenitic and duplex steels and E-nitride (Fe2N1−x) in the ferritic steel. The optically visible structure of the nitrided cases is comparable with that of the PIII layers, with higher charging densities being possible in the plasma nitriding. Also, in comparison to conventional ion implantation, large charges and parts with complicated shapes can be treated.

State-of-the-art overview: ion beam surface modification of polymers towards improving tribological properties

Abstract: Ion beam surface modification has shown great potential for improving the tribological behaviour as well as surface mechanical properties of polymeric materials. As a result, the past few years have seen many advances in the field of ion beam surface modification of polymeric materials in terms of applying conventional ion beam techniques to various types of polymers, and introducing innovative plasma-enhanced ion implantation techniques. In this paper, the main wear mechanisms of polymeric materials are first overviewed; the state-of-the-art of ion beam surface modification of polymeric materials for improving tribological as well as mechanical properties is assessed through a referenced literature review; the ion–polymer interaction mechanisms involved in ion beam modification of polymers are briefly discussed; finally, key areas for future development are suggested.

PVD coatings as an environmentally clean alternative to electroplating and electroless processes

Abstract: Today the development of clean technologies in all spheres of industrial manufacturing is an essential task, not only for material and metal finishing but also for plasma surface engineering. Among the most critical group of technologies which needs to be replaced by alternative technologies are processes used to produce functional galvanic and decorative coatings. The electroplating of finishes, such as hard chromium, cadmium and nickel in metal finishing is today recognized as a major source of environmental pollution in every country. Therefore wet bath technologies have started to lose favour compared with high performance dry coating methods such as physical vapour deposition (PVD), plasma-assisted chemical vapour deposition, chemical vapour deposition and thermal spraying. Among these techniques, the results obtained with PVD coatings in metal cutting and forming in the last 15 years show the most promising solution of the complicated situation in which galvanic coatings seemed to be technologically and economically irreplaceable. In this paper the general situation in this field is shown. Already today it is possible to replace efficiently some of the galvanic processes in specific cases (e.g. Cr, Ni, Cd, Zn, Au). It is important to point out that PVD is considered to be a technique which can provide not only metallic, but also alloyed and ceramic coatings with a virtually unlimited range of chemical composition and therefore controlled protective, mechanical and wear-resistant properties. Entering into competition with galvanic coatings the manufacturers of PVD coaters were confronted with new requirements: a huge quantity of substrates of the same size, to be chemically and plasma cleaned and then coated at the highest possible deposition rate. For industrial mass production one can therefore use only large PVD batch systems or in-line coaters. The alternative for today's low price galvanic coatings is therefore dry and clean PVD technologies, fully supported by legislation on environmental protection. The economics depend directly on the substrate type and the quantity. The first positive results on the replacement of electrodeposited nickel on aluminium substrates and hard chrome on soft iron are also reported here. A soldering test was made on a sputtered nickel layer. Wear and corrosion tests were performed with iron cores, coated with PVD CrN coating. All tests were made in the Slovenian automotive industry. Results show that for a large number of substrates PVD clean technology is already economically competitive with galvanic coatings.

Approaches to rid cathodic arc plasmas of macro-and nanoparticles : a review

Abstract: A major obstacle for the broad application of cathodic arc plasma deposition is the presence of micro- and nanoparticles in the plasma, also often referred to as 'macroparticles'. This paper reviews the formation of macroparticles at cathode spots, their interaction with the arc plasma and substrate, and macroparticle separation and removal from the plasma by various filtering methods. Nineteen variants of filters are discussed, including Aksenov's classic 90{sup o}-duct filter, filters of open architecture, and the concept of stroboscopic filtering.

Mechanical properties and oxidation resistance of nanocomposite TiN–SiNx physical-vapor-deposited thin films

Abstract: Thin films of TiN–SiN x have been prepared by reactive unbalanced magnetron sputtering from two opposite Ti and Si targets. The silicon concentration in the deposited coatings is varied between 0 and 16 at.%. The deposited films are composed of TiN nanocrystallites embedded in an amorphous SiN x matrix. These nanocomposite coatings exhibit improved mechanical properties in comparison with TiN deposited under the same conditions. Whereas the hardness measured by nanoindentation is about 27 GPa for TiN, it reaches 38 GPa in TiN–SiN x films containing 5 at.% Si and decreases to the values of amorphous SiN x at silicon concentrations above 15 at.%. Besides higher hardness values and improved wear resistance, these composite coatings are superior to TiN in their resistance against oxidation. The oxidation resistance is gradually enhanced by increasing the silicon concentration in the films. At 800°C in air, TiN–SiN x films with an Si content as low as 5 at.% exhibit a one order of magnitude lower oxidation rate compared with that of TiN. This oxidation resistance improvement is explained by the presence of the amorphous SiN x phase at the TiN grain boundaries, which limits the oxidation in these high diffusion paths and prevents recrystallization of TiO 2 .

Raman microscopic studies of PVD hard coatings

Abstract: A series of PVD ceramic hard coatings (TiN, ZrN, TiAlN, TiZrN and TiCN) were deposited on steel substrates using the cathodic arc/unbalanced magnetron deposition technique. These coatings were characterised using Raman microscopy to elucidate the behaviour of the optic and acoustic phonon modes of the (cubic) crystalline lattices. Defect-induced first- (and second-) order spectra have been observed in the 200–300 and 500–800 cm −1 regions and these have been assigned and correlated with coating composition. Changes in the position, intensity and shape of the principal TO band (640–560 cm −1 ) have been interpreted. Raman microscopy has been shown to be a very useful non-destructive complementary technique to XRD for the characterisation of PVD hard coatings.

Further investigation of the structure and properties of austenitic stainless steel after plasma nitriding

Abstract: A series of plasma nitriding experiments has been conducted on AISI 304L austenitic stainless steel at temperatures ranging from 375 to 475°C using pulsed-DC plasma with different pulse duty cycles, N2–H2 gas mixtures and treatment times. It is shown that a wide range of treatment parameters exist that allow the formation of the S-phase. The formation and growth of this surface layer depend strongly on the treatment parameters, such as nitrogen partial pressure and duty cycle. Within the parameter range investigated, the layer growth appears to be diffusion controlled with an activation energy about 107 kJ/mol. The formation of CrN precipitates during plasma nitriding is not accompanied by the formation of bcc iron, which might be expected due to the loss of free chromium. However, the S-phase transforms into CrN and bcc iron following a heat treatment at 450°C or higher for 25 h. The wear rate after plasma nitriding is greatly reduced compared with the untreated material.

New hard/lubricant coating for dry machining

Abstract: Environmental and economic considerations have emphasized the trend for more dry machining. Advanced wear-resistant coatings with increased oxidation resistance such as PVD TiAlN offer an advantage for dry machining of cast iron and alloyed steel. Although some important cutting operations are still not possible without coolants, further possibilities for dry drilling and tapping of steels are enabled by the recent approach using tools with hard coating layers topped with a lubricant layer. The combination of hard/soft coating layers allows improved chip flow with a lowered coefficient of friction and reduced cutting force. In this work, the hard/soft coating consists of a low-internal-stress TiAlN (hard layer) and WC/C (lubricant layer) of medium microhardness and low coefficient of friction. Both coating types are produced economically and reproducibly in one production scale PVD coating system. Recent performance data from field tests will be presented.

Structural properties, internal stress and thermal stability of nc-TiN/a-Si3N4, nc-TiN/TiSix and nc-(Ti1−yAlySix)N superhard nanocomposite coatings reaching the hardness of diamond

Abstract: The average crystallite size, d, in the range of about 3–8 nm determined from XRD by means of the Scherrer formula and integral width of the Bragg peaks compares well with that determined from the Warren–Averbach analysis. TiN films show (200) texture which changes to random orientation of the crystallites when the silicon content reaches about 10 at.%. The biaxial stress of ≤0.4 GPa for ≤10 μm thick films is fairly low. The random stress determined from the Warren–Averbach analysis increases with decreasing crystallite size from about 1 GPa for d ≥10 nm to almost 10 GPa for d≈3 nm. A strong increase is observed for the stability of the nanostructure and of the hardness upon annealing: the recrystallization temperature increases from about 850°C for d≥5 nm to ≥1150°C for d≤3 nm. This is explained by thermodynamical stabilization of the grain boundaries due to segregation. Superhardness remains constant up to recrystallization. For superhardness of about 100 GPa, the elastic modulus of 70–500 GPa and the universal hardness of about 17–22 GPa (loads between 30 and 100 mN) compare well with the hardness of a single-phase nanocrystalline diamond. Besides this extremely high hardness, the coatings also have a very high toughness and elastic recovery of 80–90%.

ZrN/Cu nanocomposite film—a novel superhard material

Abstract: This article reports on the structure and hardness of ZrCu‐N films prepared by dc reactive magnetron sputtering of a ZrCu alloyed target in a mixture of Ar+N 2 using a round planar unbalanced magnetron of diameter 100 mm. It was found that there is a strong correlation between the structure of the film and its hardness. The hard (<40 GPa) ZrCu‐N films are characterized by many weak reflections from poly-oriented ZrN and Cu grains. In contrast, the superhard (µ40 GPa) ZrCu‐N films are characterized by a strong reflection from ZrN grains with a dominate ZrN(111) orientation and no reflections from Cu. The superhard ZrCu‐N films with a hardness of 54 GPa are nc-ZrN/Cu nanocomposite films composed of strongly oriented ZrN grains surrounded by a thin layer of Cu. These films exhibit a high elastic recovery of about 80% (determined by a microhardness tester) and contain approximately 1‐2 wt.% Cu. The superhard nc-ZrN/Cu nanocomposite films represent a new class of superhard materials of the type nc-MeN/metal. © 1999 Elsevier Science S.A. All rights reserved.

Structure, mechanical and tribological properties of nitrogen-containing chromium coatings prepared by reactive magnetron sputtering

Abstract: Cr1−xNx coatings were deposited by magnetron sputtering at a substrate temperature of 200°C onto AISI 316 stainless-steel substrates immersed in an Ar/N2 plasma. The goal of this investigation was to study the influence of nitrogen content on the structural, mechanical and tribological properties of the Cr1−xNx coatings (with x being in the range of 0–0.4). The coating composition and microstructure were evaluated utilizing glow discharge optical emission spectroscopy and glancing angle X-ray diffraction, whereas the morphology was evaluated by scanning electron microscopy. Knoop microhardness, scratch adhesion, pin-on-disc sliding, ball-on-plate impact and abrasive wheel wear tests were performed to evaluate the mechanical and tribological properties. The presence of Cr, Cr2N, CrN (and mixtures of these phases) has been identified and related to the film composition. For Cr1−xNx coatings with x≤0.16, only the α-Cr phase could be detected. A progression towards a denser microstructure was found with increasing nitrogen content up to x=0.29, associated with an increase in hardness from 700 up to 2400 HK0.025. Cr1−xNx coatings with x=0.10–0.16 showed good adhesion and the best abrasive and pin-on-disk sliding wear resistance, together with less crack development around the indentation area (and thus improved toughness) in impact tests after 50 000 impacts, against both steel and cemented tungsten carbide balls. The hardest coating (Cr0.71N0.29) performed best in terms of reducing the resulting impact indentation volume.

Tribological properties of nanocrystalline diamond films

Abstract: In this paper, the authors present the friction and wear properties of nanocrystalline diamond (NCD) films grown in A-fullerene (C{sub 60}) and Ar-CH{sub 4} microwave plasmas. Specifically, they address the fundamental tribological issues posed by these films during sliding against Si{sub 3}N{sub 4} counterfaces in ambient air and inert gases. Grain sizes of the films grown by the new method are very small (10--30 nm) and are much smoother (20-40 nm, root mean square) than those of films grown by the conventional H{sub 2}-CH{sub 4} microwave-assisted chemical-vapor-deposition (CVD) process. Transmission electron microscopy (TEM) revealed that the grain boundaries of these films are very sharp and free of nondiamond phases. The microcrystalline diamond (MCD) films grown by most conventional methods consist of large grains and a rough surface finish, which can cause severe abrasion during sliding against other materials. The friction coefficients of films grown by the new method (i.e., in Ar-C{sub 60} and Ar-CH{sub 4} plasmas) are comparable to those of natural diamond, and wear damage on counterface materials is minimal. Fundamental tribological studies indicate that these films may undergo phase transformation during long-duration, high-speed and/or high-load sliding tests and that the transformation products trapped at the sliding interfaces can intermittently dominate friction and wear performance. Using results from a combination of TEM, electron diffraction, Raman spectroscopy, and electron energy loss spectroscopy (EELS), they describe the structural chemistry of the debris particles trapped at the sliding interfaces and elucidate their possible effects on friction and wear of NCD films in dry N{sub 2}. Finally, they suggest a few potential applications in which NCD films can improve performance and service lives.

A comparative study of adhesion test methods for hard coatings

Abstract: The feasibility of seven techniques for testing and evaluating the adhesion of thin films was investigated: scratch test, four-point bending test, Rockwell test, cavitation test, impact test, laser-acoustics and acoustic microscopy The studies were performed with TiN films (thickness 12–245 μm) deposited on the annealed steel 42CrMo4 The adhesion of the TiN films was varied by varying the time of pre-sputtering the steel substrate with argon ions before the film deposition Argon pre-sputtering for 15 min is recommended to guarantee an optimal adhesion The pre-sputtering time, tS, was reduced down to 05 min to reduce the adhesion The following test parameters were used to evaluate the adhesion: the friction work, acoustic emission activity and critical load of the scratch test, the critical strain and the defect density of the four-point bending test, the proportional damage area of cavitation test, the critical number of loading cycles of the impact test, and Young's modulus of the film measured with the laser-acoustic method These test parameters were examined for any correlation with the pre-sputtering time, tS The results are summarized in a table that shows which test methods and test parameters yield corresponding and contradictory evaluations of the film quality The effect of defect density and residual stresses is discussed Laser-acoustics and acoustic microscopy are non-destructive methods Young's modulus, as measured by laser-acoustics, is sensitive to the density of micro-defects This is expected to indicate their effect on the adhesion

Characterization of sputter-deposited chromium oxide thin films

Abstract: Cr 2 O 3 thin films exhibit high hardness values and low friction coefficients. These properties make chromium oxide a serious candidate to replace transition metal nitrides or Al 2 O 3 in special applications. The CrO x films were deposited on silicon, glass and HSS substrates by r.f. reactive magnetron sputtering at different oxygen partial pressures and substrate temperatures, T S , between 360 and 590 K. The crystallographic phase was determined by X-ray diffraction analysis. Polycrystalline films with a single α-Cr 2 O 3 phase are obtained in the range between 15 and 25% oxygen in the sputtering gas at a T S value exceeding 500 K. The surface morphology was examined by atomic force microscopy and revealed a very low roughness on amorphous films. The chemical composition was measured by electron probe microanalysis. The grain size varied significantly with the oxygen content and the substrate temperature. The optical constants and the optical band gap of crystalline films were determined by spectroscopic ellipsometry in the photon energy range of 1.5–5.0 eV. The optical constants appeared to be extremely sensitive to the chemical composition of the Cr 2 O 3 films. Hardness values up to 32 GPa were obtained by nanoindentation at compressive residual stress levels below 1 GPa. Mixed phase CrN/Cr 2 O 3 thin films combine the high hardness of Cr 2 O 3 and the toughness of CrN.

Large area glass coating

Abstract: Since the end of the seventies vacuum coating technology for the deposition of optical thin films on large area glass substrates has enjoyed a steady growth. Nowadays, the main applications are low emissivity and solar control thin film systems on architectural glass as well as transparent electrodes for flat panel displays. Future markets like electrochromic or anti-reflective coatings appear on the horizon; the latter covering a wide range of products like picture frames, show-cases, shop windows, and all kinds of data and TV screens. The paper gives an introduction into the above-mentioned applications and outlines the present state of sputtering technology for large area glass coating.

Effects of deposition temperature and thermal cycling on residual stress state in zirconia-based thermal barrier coatings

Abstract: Advanced ceramic multilayered coatings are commonly used as protective coatings for engine metal components to improve performance, e.g. thermal barrier coatings (TBCs). Zirconia-based TBCs were produced by plasma spraying process and characterized in terms of microstructure, porosity, elastic modulus, adherence and residual stresses. In this contribution the residual stresses in multilayered coatings applied on Ni based superalloys for use as thermal barrier coatings were studied both by numerical modelling and experimental stress measurement. The thermal residual stresses generated during the spraying process of duplex TBCs were simulated by using an heat transfer finite element program and an elasto-plastic biaxial stress model. The TBC system was subjected to different thermal cycling conditions (maximum temperature, heating up and cooling down rates, dwell time at maximum temperature, etc.). The stress distribution within the TBC was also modelled after thermal cycling. The stress state in the as-deposited and in thermally cycled coatings was verified using an X-ray diffraction technique. The measurements were in good agreement with the residual stress modelled calculations. It was observed that the residual stresses were dependent on the thermal history of the TBC (as-deposited and thermally cycled). It is proposed that thermal cycling allowed the stresses to relax by microcracking and creep mechanisms at high temperature such that on cooling down to room temperature, an in-plane biaxial compressive stress will arise on the zirconia top coating due to the difference on the coefficients of thermal expansion between the metallic substrate and ceramic coating material.

Microstructure and properties of nanocomposite Ti-B-N and Ti-B-C coatings

Abstract: Superhard nanocomposite coatings are currently of great interest for wear protection of tools. Within this work, after some consideration of the design and failure of nanocomposites, results on nanocomposite Ti–B–N and Ti–B–C films are presented and discussed. Coatings with different compositions in the quasi-binary systems TiN–TiB 2 and TiC–TiB 2 were deposited onto austenitic stainless steel and molybdenum sheets by means of unbalanced d.c. magnetron co-sputtering using segmented TiN/TiB 2 and TiC/TiB 2 targets. Coating chemical, structural and mechanical properties were investigated using electron-probe microanalysis (EPMA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD), and depth-sensing nanoindentation. Coatings with elemental compositions of about 35–45 at.% Ti, 18–44 at.% B and 20–36 at.% N or 22–40 at.% C consist of a nanocrystalline arrangement of TiB 2 and TiN or TiC, respectively, with crystallite sizes of 1–5 nm. Coating hardness varies between 50 and 70 GPa and elastic moduli are close to 500 GPa.

Recent advances in magnetron sputtering

Abstract: The paper will outline the historical development of sputtering techniques up to the recent development of closed-field unbalanced magnetron sputtering (CFUBMS). Examples will then be given of the use of CFUBMS to develop advanced coatings for industrial applications, including corrosion resistant coatings for aerospace, hard ceramic coatings for wear resistance, and coatings with novel thermal and chemical properties. Finally, current development in the technology and in understanding of the principles of the process will be described.

High intensity pulsed ion beam sources and their industrial applications

Abstract: This paper presents research on practical applications of high intensity pulsed ion beams (HIPIBs) investigated at the Nuclear Physics Institute of the Tomsk Polytechnic University (NPI TPU) and the Scientific Industrial Enterprise ‘Linetron’, N. Novgorod. The most interesting scientific results have been obtained in the following fields: • HIPIB surface modification for the increase of wear resistance of tools; • deposition of thin metal, composite and diamond-like carbon (DLC) films; • short-pulse ion implantation in semiconductors. It was shown that ion beams with relatively low power density (10 6 –10 9 W/cm 2 ) are very promising for industrial applications. The paper presents a brief description of the HIPIB–solids interaction and main HIPIB parameters used in the research, as well as modification of properties of treated samples.

Effects of Al content on hardness, lattice parameter and microstructure of Ti1-xAlxN films

Abstract: Ti1−xAlxN films were synthesized by the arc ion plating method using Ti1−xAlx alloy targets with differing Al contents. X-ray diffraction patterns from films indicated that the NaCl structure for x≤0.6 changed into wurtzite structure for x≥0.7. For films with x≤0.6, the lattice parameter decreased in proportion to the x value, and correspondingly, the hardness gradually increased from ∼2000 HV for x=0 up to 3200 HV for x=0.6. On the other hand, the hardness of films with x≥0.7 abruptly deceased from ∼3000 HV for x=0.7 to 1400 HV for x=1. Further, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that the films with x=0.6 had a typical columnar structure with grain sizes of 100–200 nm. While for films with x≥0.7, a columnar structure disappeared and excess Al atoms did not segregate at the grain boundaries as AlN, but Ti and Al were uniformly dissolved and distributed as nitride grains with wurtzite structure.

Biomaterials modification by ion-beam processing

Abstract: Biomaterials modification by ion-beam processing is becoming popular for improving medical device function, biocompatibility and as a new mutation breeding method. Ion-beam-based processes, such as ion implantation and ion-beam assisted deposition (IBAD) can provide beneficial surface layers with desirable properties without detrimentally affecting the bulk properties. Ion implantation has been successful in biomaterials modification, such as in improving the wear resistance of artificial joint components, in improving wettability, anticoagulability, anticalcific behavior of biomedical polymers, and in minimizing biofouling of medical devices, etc. IBAD has been used to prepare hydroxyapatite coatings with high adhesive strength on substrates of several implant materials. Biocompatible diamond-like carbon coatings and C–N films, antibacterial coatings and sealant coatings have also been produced by this technique. This paper reviews the present status of applications of the ion-beam process in modifying the surface of biomaterials, as well as the effects induced by ion-beam irradiation to crop seeds, cells and microbes.

Mechanical and tribological evaluation of PVD WC/C coatings

Abstract: Five different WC/C coatings deposited by physical vapour deposition (PVD) on high speed-steel (HSS) have been evaluated with respect to their mechanical and tribological properties. For all coatings a chromium layer was deposited first to enhance coating adhesion. The carbide phase (WC) and the carbon (C) phase were deposited simultaneously by direct-current magnetron sputtering of a WC target and plasma-assisted chemical vapour deposition using hydrocarbon gas, respectively. The influence of the chromium interface layer thickness, the amount of WC phase and the flow of hydrocarbon gas on the mechanical and tribological properties of the coatings have been investigated. The coatings have been characterised with respect to their chemical composition (glow discharge optical emission spectroscopy), hardness (Vickers microhardness), morphology (scanning electron microscopy, SEM), roughness (profilometry), residual stress (beam bending), critical load (scratch testing) and abrasive wear resistance (the “dimple grinder test”). Furthermore, a ball-on-plate test was employed to obtain information about the frictional properties and sliding wear resistance of the coatings. The wear mechanisms and wear debris were analysed by SEM, Auger electron spectroscopy and electron spectroscopy for chemical analysis. All WC/C coatings displayed a thickness between 2 and 4 μm and a surface roughness in the range of 10 to 70 nm. The hardness varied between 1500 and 1800 HV. The coating residual stress was found to range from −2.5 to −0.5 GPa. The scratch test revealed a relatively high critical normal load, i.e., a relatively good adhesion of the WC/C coatings to the HSS. The abrasive wear resistance was found to be very high, in fact equally as high as that of PVD TiN. In the sliding wear test it could be seen that the coating containing the lowest amount of carbide phase (WC), i.e., the highest amount of carbon phase (C), and which had the highest compressive residual stress yielded the lowest friction and wear rate against steel. In addition, this coating was also found to yield the lowest wear rate of the counter material. In summary, a WC/C coating with overall good mechanical and tribological properties was obtained provided a relatively thin chromium layer was deposited first and if a relatively high acetylene gas flow was utilised during deposition of the WC/C layer.

Thermal stability of diamond-like carbon films with added silicon

Abstract: Diamond-like carbon (DLC) films with added silicon content from 0 to 19.2 at.% were deposited using r.f. PECVD (radio frequency plasma enhanced chemical vapor deposition). Fourier transform IR (FTIR) spectrometry, Raman spectrometry and X-ray photoelectron spectrometry (XPS) were used to determine the structural change of the annealed DLC films in ambient air. By increasing the annealing temperature the CHn and Si–H groups in the FTIR spectra decrease because of hydrogen evolution, whereas the intensities of CO and Si–O peaks increase owing to oxidation. From Raman spectra, the integrated intensity ratio ID/IG of the pure DLC films and the silicon-doped films increases at 300 and 400 °C, respectively, whereas the observable shoulder of the D band occurs at 400 and 500 °C, respectively, which indicates that the addition of silicon improves the thermal stability of DLC films. Using XPS analysis, a surface reaction for the annealed films is investigated.

Functionalized coatings based on inorganic–organic polymers (ORMOCER®s) and their combination with vapor deposited inorganic thin films

Abstract: Hybrid polymers (ORMOCER ® s) with inorganic and organic structural units can be used to generate new functionalized coatings on a variety of substrates (ceramics, metals, polymers, etc.). By processing at temperatures below 150 °C, the formation of both inorganic and organic network structures using the sol–gel approach is possible. Due to the incorporation of special organic functional groups, important application related properties can be accomplished. ORMOCER ® lacquers can be processed by nearly all conventional coating techniques (dipping, spraying, spin on, etc.). The basic application fields for ORMOCER ® coatings are: • abrasion and scratch resistance, decoration; • barrier layers for packaging, corrosion resistant layers; • antisoiling, antifogging, antistatic and antireflective applications. In the past two years, the combination of ORMOCER ® layers with vapor deposited inorganic thin films (e.g. SiO x ) has been investigated, especially for barrier applications. Outstanding barrier properties were achieved, which show synergetic effects by using two different coating techniques together (wet chemical processing, vapor deposition).